Hi, I just took out an old A64 rev B with the same extension and figured out the same thing.
My model is a "Pine64 PINE A64+"
What's cat /proc/device-tree/model telling you about your exact model?
I don't think youi'll have to compile your own kernel to fix this and that updating the devicetree should be sufficient. I have already patched my devicetree to enable uart 1 to 4.
That I did the hacky way, locating the sun50i-a64-pine64-plus.dtb, then decompiling it dtc -I dtb -O dts -i sun50i-a64-pine64-plus.dtb -o sun50i-a64-pine64-plus.dts, then replacing some status = "disabled"; lines with status = "okay"; and then compiling back to dtb: dtc -I dts -O dtb -i sun50i-a64-pine64-plus.dts -o sun50i-a64-pine64-plus.dtb.
It's sure nicer to directly compile your devicetree from the sources I just didn't have them handy at a time. I left the board at a friends but I'll let you know once I got the wifi working.